The present invention concerns catheters used for the treatment of cardiac arrhythmias. More specifically, the present invention relates to a novel ablation catheter having an electrode temperature monitoring system.
Cardiac arrhythmias are often caused when portions of the heart form alternative conduction pathways which transmit electrical signals that interfere with the normal conduction of electrical signals which regulate the beating of the heart. In order to treat cardiac arrhythmias stemming from this problem, the cells which comprise these alternative conduction pathways must either be destroyed or the conductive pathways from these cells be blocked from transmitting electrical signals to the rest of the heart.
One way to treat this ailment is through the use of a procedure called Radio Frequency Ablation (RFA). The procedure entails first mapping the heart in order to determine where these alternative conduction pathways are located. Once these alternative conduction pathways are located, radio frequency (RF) waves are then used to create lesions in the heart which either destroys the cells that comprise these alternative conduction pathways or which blocks the conduction of electrical signals from these cells.
RFA typically involves the use of specialized ablation catheters which are designed to be inserted vascularly into a person and maneuvered into the heart. These ablation catheters carry electrodes which transmit RF waves to the tissues at an application site. The RF waves generate heat at the application site which in turn causes the cells at the application site to rupture forming a lesion in the heart tissue.
A common problem among prior art ablation catheters is the formation of coagulum around the electrodes during an RFA. As the RF waves are being delivered at the application site, both the electrode and the surrounding tissue are heated. The heat generated by the RF waves sometimes cause the electrode to overheat, causing the blood surrounding the electrode to coagulate on the electrode. The coagulum that collects on the electrode causes the impedance between the electrode and the application site to increase thereby reducing the effectiveness of the electrode to deliver the RF waves. As a result it is often necessary to stop the RFA in order to remove the coagulum from the electrode.
There are ablation catheters which currently have multiple electrodes for delivering RF energy to an application site. Many of these catheters deliver RF energy by sequentially activating the electrodes so that a linear lesion is created. The temperature of each electrode in these catheters should be monitored in order to ensure that the electrodes do not overheat and cause excess coagulum to build up. However, monitoring an electrode would typically require a temperature sensor located at the electrode and two conductive wires to relay information from the sensor. Consequently, as more electrodes are carried by the ablation catheter, more and more of the catheter""s internal area is taken up by conductive wires. The amount of conductive wires which need to travel through an ablation catheter can put limitations on the size, flexibility and maneuverability of the ablation catheter.
Accordingly, it is an object of this invention to provide an ablation catheter which is capable of monitoring the temperature of its electrodes.
Accordingly, it is also an object of this invention to provide a means for measuring the temperature of a plurality of electrodes that occupy minimal space in an ablation catheter.
To achieve these objectives, and in accordance with the purposes of the present invention the following ablation catheter is presented. As will be described in greater detail hereinafter, the present invention provides the aforementioned and employs a number of novel features that render it highly advantageous over the prior art.
In accordance with an illustrative embodiment of the present invention, an ablation catheter is provided which comprises an elongated catheter body, a plurality of electrodes, and a thermal monitoring circuit. In order to minimize the number of wires needed to monitor the temperature of the electrodes, the thermal monitoring circuit is comprised of a plurality of thermocouples joined in series. The thermal monitoring circuit will require only two wires to travel through the elongated catheter body in order to monitor a plurality of electrodes. In contrast, the prior art would typically require two wires to travel to and from each electrode.
For purposes of illustration, an embodiment of the thermal monitoring circuit is presented wherein the thermocouples are connected in series with a sensing junction and a reference junction of each thermocouple thermoconductively coupled to different electrodes. Once an electrode is activated the heat from the electrode will cause the reference or sensing junction thermoconductively coupled to the activated electrode to generate a voltage from which a temperature for the activated electrode can be calculated therefrom.
Also for the purposes of illustration, an alternative embodiment of the thermal monitoring circuit is presented. This alternative embodiment has the sensing junctions thermoconductively coupled to the electrodes while the reference junctions are disposed in a central lumen in the elongated catheter body. Once again, if only one electrode is activated, the activated electrode will cause a thermocouple to generate a voltage from which the temperature of the activated electrode can be calculated therefrom.
A more detailed explanation of the invention is provided in the following description and claims, and is illustrated in the accompanying drawings.